Influence of imperfections on tunneling rate in δ\delta-layer junctions

The atomically precise placement of dopants in semiconductors using scanning tunneling microscopes has been used to create planar dopant-based devices, enabling the exploration of novel classical or quantum computing concepts, which often require precise control over tunneling rates in their operation. While the geometry of the dopants can be defined to sub-nanometer precision, imperfections can still play a significant role in determining the tunneling rates. Here, we investigate the influence of different imperfections in phosphorous $\delta$-layer tunnel junctions in silicon: variations of $\delta$-layer thickness and tunnel gap width, interface roughness, and charged impurities. It is found that while most of the imperfections moderately affect the tunneling rate, a single charged impurity in the tunnel gap can alter the tunneling rate by more than an order of magnitude, even for relatively large tunnel gaps. Moreover, it is also revealed that the tunneling rate strongly depends on the electrical charge sign of the impurity

Electronic structure of boron and aluminum δ\delta-doped layers in silicon

Recent work on atomic-precision dopant incorporation technologies has led to the creation of both boron and aluminum $\delta$-doped layers in silicon with densities above the solid solubility limit. We use density functional theory to predict the band structure and effective mass values of such $\delta$ layers, first modeling them as ordered supercells. Structural relaxation is found to have a significant impact on the impurity band energies and effective masses of the boron layers, but not the aluminum layers. However, disorder in the $\delta$ layers is found to lead to significant flattening of the bands in both cases. We calculate the local density of states and doping potential for these $\delta$-doped layers, demonstrating that their influence is highly localized with spatial extents at most 4 nm. We conclude that acceptor $\delta$-doped layers exhibit different electronic structure features dependent on both the dopant atom and spatial ordering. This suggests prospects for controlling the electronic properties of these layers if the local details of the incorporation chemistry can be fine tuned.Comment: Main text 8 pages, 6 figures + Appendices 3 pages, 2 figure

Local Ordering in the Pseudogap State of the High-Tc_c Superconductor Bi2_2Sr2_2CaCu2_2O8+δ_{8+\delta}

We report atomic scale characterization of the pseudogap state in a high-T$_c$ superconductor, Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$. The electronic states at low energies within the pseudogap exhibit spatial modulations having an energy-independent incommensurate periodicity. These patterns, which are oriented along the copper-oxygen bond directions, appear to be a consequence of an electronic ordering phenomenon--the observation of which correlates with the pseudogap in the density of electronic states. Our results provide a stringent test for various ordering scenarios in the cuprates, which have been central in the debate on the nature of the pseudogap and the complex electronic phase diagram of these compounds.Comment: To appear on Science Express, http://www.sciencemag.org/sciencexpress/recent.shtml, 19 pages, 4 figures, pdf onl

Stochastic magnetic actuated random transducer devices based on perpendicular magnetic tunnel junctions

True random number generators are of great interest in many computing applications such as cryptography, neuromorphic systems and Monte Carlo simulations. Here we investigate perpendicular magnetic tunnel junction nanopillars (pMTJs) activated by short duration (ns) pulses in the ballistic limit for such applications. In this limit, a pulse can transform the Boltzmann distribution of initial free layer magnetization states into randomly magnetized down or up states, i.e. a bit that is 0 or 1, easily determined by measurement of the junction's tunnel resistance. It is demonstrated that bitstreams with millions of events: 1) are very well described by the binomial distribution; 2) can be used to create a uniform distribution of 8-bit random numbers; 3) pass multiple statistical tests for true randomness, including all the National Institute of Standards tests for random number generators with only one XOR operation; and 4) can have no drift in the bit probability with time. The results presented here show that pMTJs operated in the ballistic regime can generate true random numbers at GHz bitrates, while being more robust to environmental changes, such as their operating temperature, compared to other stochastic nanomagnetic devices.Comment: 8 pages, 3 figures, 2 tables, will be submitted to peer-reviewed journa

Impact Assessment and Yield Gap Analysis of Composite Fish Culture Technology in North East Region with Special Reference to Arunachal Pradesh, India

The North Eastern States (NES) are the easternmost region of India among them Arunachal Pradesh is a largest hill state and shares its international boundaries with Bhutan in the west, China in the north and Myanmar in the east with a wide range of climates and altitudes. Fish farming is playing a vital role from economic, nutritional and employment point of view in the state, in spite of increase in the production, the current level of fish production is not sufficient to fulfil the requirement, very much far-away to meet out the present consumption demand. Therefore, to identify the yield gap and adoption gap of improved production practice of composite fish culture technology the present study was conducted in the West Kameng district of Arunachal Pradesh. It has been observed that the yields obtained by the farmers are well below those obtained in Govt. Farms and OFT/FLD trials. Carp cultivation practices of 171 farmers were examined on the basis of multistage random sampling. The sample was collected from all the administrative circle of the district West Kameng of Arunachal Pradesh NER India. The average production obtained by the respondents were found only 1.09 t/ha annually, but the range was 2.0 to 2.4-2.8 t/ha in the trials of Govt. farms and OFT/FLDs. The difference of 1.31t/h constituted yield gap under normal practices, these differences were observed due to critical fish farming input availability lacuna on time, the extent to which the farmers adopted the recommended practices, and other socio-economic factors. The study thus clearly showed that the gap is due to the deficiency in adopting the technology along with timely un-availability of quality fish seed and feed which may be bridged only by promotion of the region specific tailored suitable technology of fish farming along with assurance for availability of critical inputs on time